This invention concerns a heat exchanger wherein the material which comprises the heat exchange surface structure contains at least one layer of a thermotropic liquid crystalline polymer and at least one layer of an isotropic thermoplastic.
Heat exchangers are common pieces of equipment, used in many applications, such as chemical processes, in automotive uses, household uses, and others. Heat exchangers are most commonly used to transfer heat between two fluids such as two liquids, a liquid and a gas, or between two gases. Traditionally, the materials used for the heat exchange surfaces are metals, which usually have relatively high thermal conductivities and good strength. However metals have certain drawbacks, such as high forming and assembly costs, relatively high densities and therefore high weights, and sometimes poor corrosion resistance.
To overcome some of these disadvantages, heat exchangers using plastics have been developed. For instance, in highly corrosive environments heat exchangers using polytetrafluoroethylene (or perfluorinated tetrafluoroethylene copolymers) have been used. However plastics have some inherent disadvantages, such as poorer heat transfer coefficients, in some cases relatively poor chemical stability, and permeability to the gas(es) or liquid(s) which contact the heat exchange surfaces. However, they often offer the advantages of lighter weight and easier fabrication than metals. Therefore, improved plastic heat exchangers are being sought.
Japanese Patent Application 03/007891 describes a heat exchanger tube made from a liquid crystalline polymer and a filler having high heat conductivity. No mention is made of a tube having multiple layers of polymers.
French Patent Application 2,566,107 describes heat exchanger panels made from polymers such as polyethylene. No mention is made of layered plastics or LCPs.
U.S. Pat. Nos. 4,923,004, 4,955,435, 5,275,235 and 5,316,078 describe heat exchangers which employ various polyamides for the heat exchange surface materials. Thermotropic liquid crystalline polymers are not mentioned in these patents.
D. A. Reay, Heat Recovery Systems and CHP, vol. 9, p. 209-16 (1989), and I. H. Gross, Proceedings of Antec ""93, p. 964-968 (1993) describe the use of polymers in heat exchangers. No mention is made of using layered polymer structures, nor of using LCPs.
This invention concerns, a heat exchanger containing a heat exchange surface material, comprising, a layer of a thermotropic liquid crystalline polymer and a layer of a thermoplastic.
This invention also concerns a heat exchanger panel wherein a heat exchange surface material comprises a layer of an isotropic polymer and a thermotropic liquid crystalline polymer.
By a heat exchange surface material (HESM) is meant a material which is used as part of a heat exchanger or a component thereof, and which is the material through which the major portion of the heat that is exchanged between the two fluids (gas or liquid) is meant to flow. It also performs the function of keeping the two fluids between which heat is being exchanged apart.